DNA DAMAGE AND REPAIR IN CHICK-EMBRYO CELLS FOLLOWING X-IRRADIATION INVITRO AS COMPARED TO MAMMALIAN-CELLS - BIOCHEMICAL AND PHYSICOCHEMICAL INVESTIGATIONS

Brain cells (b-cells) and liver cells (l-cells) of the chicken embryo and thymic cells (t-cells) of the rat were X-irradiated in vitro at do ses of 1.25-50 Gy. When compared to t-cells, b- and l-cells exhibited 1) a lower stimulation of poly (adenosine diphosphate-ribose) transfer ase and unscheduled DNA synthesis following X-irradiation, 2) an almos t fivefold higher inhibition of semiconservative DNA synthesis, 3) a l ess condensed chromatin, 4) about fourfold higher threshold doses with regard to significant effects on nucleoid sedimentation and viscometr y of alkaline cellular lysates, and 5) an apparently two- to threefold lower DNA repair during a 30 min post-exposure repair period. The res ults suggest that the lower radiation sensitivity of chicken embryo ce lls is attributable to an initial mechanism of DNA repair and/or DNA p rotection which may be closely connected to minor chromatin compactnes s and higher intrinsic activities of repair enzymes.